answered by experiment; and we must take care not to be biassed by the presence of glycine in the bile, combined with choleic acid as glycocholic acid.

So far the observations are clear that, if benzoic, cinnamic, nitrobenzoic acids, or any substances containing them, are taken internally, they appear in the urine as hippuric and nitrohippuric acids. But, as the food of most people does not contain any benzoic acid as far as we know, the regular appearance of hippuric acid cannot be the consequence of diet only. Even Duchek found that his greengages did not contain a sufficient quantity of benzoic acid to account for the whole amount of hippuric acid found in his urine after eating them; and he therefore takes refuge in a supposition, that there was another compound of benzoyle present in the fruit, which was capable of forming hippuric acid. The strongest argument has been brought by Liebig. The urine of cows is always equally rich in hippuric acid, no matter whether they feed on hay or on mangel wurzel. Now, as the latter has been found by direct analysis, and by experience in the manufacture of sugar, not to contain any benzoic acid, we cannot draw any other conclusion from the presence of hippuric acid in the urine of herbivora and of man, than that it is a product of the organism, to the formation of which the elements of the food give the materials. Proust and Guckelberger3 both observed the formation of bitter oil of almonds, and, secondarily, of benzoic acid, as one of the products of oxydation of albuminous substances. We may, therefore, by analogy, think it possible that the oxydation of albuminous substances in the body may yield some benzoic acid, as a collateral product, in small quantity. These considerations point to a difference between the oxydation of albuminous substances in herbivorous animals and in carnivora. The urine of the latter has not been observed to contain any hippuric acid, and the urine of cows always contains this acid, even when their food is decidedly free from benzoic acid. The explanation of this difference, if it really exist, will have to be sought by further experiments.

Regarding the physiological bearing of hippuric acid in animals, the observations seem to show that rest and activity, as well as different descriptions of food, have a considerable influence upon the quantity in which it is found in the urine. According to Liebig, rest seems to favour the production of

hippuric acid, and the urine of horses contains a larger amount of it when they are not overworked. In accordance with this statement, Erdmann and Marchand found the urine of horses kept for private use to contain much hippuric acid; that of horses used for ploughing, however, contained only benzoic acid. Hutstein2 also observed that the urine of private horses, which had yielded hippuric acid exclusively, contained only benzoic acid after they were used for hard work. Dr. G. Birds says that both hippuric and benzoic acids will disappear from the urine of over-driven animals. He could not detect a trace of either in the urine of an ox which had been driven up from the country to Smithfield, and killed a few hours after.

The influence of some descriptions of food has been investigated by Landerer, who found that the urine of horses would only yield hippuric acid while they were fed on oats and hay, and did not yield any while fed on barley and straw. Riley also found the urine of calves to yield hippuric acid only while feeding on grass or hay; and Schwartz observed that the urine of cows contained only traces of hippuric acid when fed on the residue from the distillation of spirits.

The occurrence of benzoic acid in the fresh urine of animals is at least problematical. Much more problematical, however, is rendered the influence of either work or rest upon the quantity of hippuric acid secreted by animals, through the following statements of Roussin.8 He found that horses fatigued produce much hippuric acid, and little urea. Horses well fed and quiet produce little or no hippuric acid; urea, on the contrary, is found in their urine in very large proportions. The limpidity of the liquid may be the index. If it be clear, and deposit little carbonate of lime, it has much urea and little hippuric acid; if it be muddy, it is certain that there is much hippuric acid. Upon this fact Roussin builds a speculation on the transformation of hippuric acid into urea, and vice versa, the very nature of which, however, makes the character of his analyses still more doubtful than they appear at first sight, from the fact of their being in direct opposition to the results of the analyses enu

Ann. d. Chem. und Pharm.,' liv, p. 31.

Gorup-Besanez, loc. cit., p. 171.

I have taken this from an extract in the American Journal of Science and

Art,' July, 1856, No. 61, p. 102.

merated above. In the following analyses he determined the urea in the form of the dry nitrate:

These analyses should be repeated with the whole of the urine discharged in twenty-four hours; in other words, with regard to time. The urea is, moreover, to be determined by a more accurate method than that through the antiquated nitrate.

Pathological occurrence.

The case of a girl, suffering from chorea, who lived on apples, bread, and water, and discharged an excess of hippuric acid, has been recorded by Pettenkofer.1 In a case by Bouchardat, milk diet is blamed as the cause of a discharge of two parts, in a thousand of the urine, of hippuric acid, by a woman suffering from a variety of severe disorders. A case observed by Dr. Garrod2 relates to a young man who, under certain circumstances, discharged a urine which, on the addition of an acid, yielded crystals of hippuric acid. Half a pint of urine yielded 40 grains of the acid. No information as to the source of the hippuric acid could be obtained from the history of the patient. It is denied that he had ever taken any benzoic acid, so that, if no imposition was practised by the patient, there is at all events some mystery about his case.

A large quantity of hippuric acid is present in the acid urine of fever patients, of which it is said to cause, in part at least, the acid reaction. The observer of this fact, Lehmann, has also found hippuric acid in diabetic urine, in every instance in which he has sought for it. In one instance 100 parts of urine yielded 0.025 parts of crystallized hippuric acid. I

Ann. d. Chem. und Pharm.,' lii, p. 86.

2 Originally communicated in Dr. G. Bird's work, p. 303. The first two cases may also be consulted there in detail.

have already mentioned that Hánefeld and Duchek have confirmed Lehman's observations.

The last observation is that of Schlossberger, already mentioned. He found hippuric acid in the scales of ichthyosis. We have not yet been informed whether it was accidentally present in a single case, or whether it is of frequent or constant occurrence in that disease.

The reader will think this a very unsatisfactory chapter, and so indeed it is. We want observations, for which there is a large field open. But undoubtedly some technical difficulties will have to be overcome first, before the analysis of hippuric acid can be made with sufficient accuracy.

CHAPTER VIII.

CHLORINE AND CHLORIDES.

Remarks on the Incineration of Urine.

THE solid residue of the evaporation of urine, when exposed to a red heat for the necessary length of time after the complete combustion of all organic ingredients, leaves an ash, which is made up of the so-called incombustible salts. Accurate analysis has shown that this ash does not contain the inorganic salts in the same condition in which they were dissolved in the urine; from which we must conclude that, under the united influences of heat, the oxygen of the air, and the reducing quality of the charred animal matter, they have undergone certain considerable changes. The acid phosphate of soda, for example, when intimately mixed with carbon, will, under the influence of red heat, give off a part of its acid, which is reduced at the same time, and volatilized in the form of phosphorus and carbonic acid. But the most considerable loss which the fixed salts incur by the process of incineration is that of chlorine. Indeed so considerable is this loss, that Becquerel found, as the average quantity of chlorine discharged by healthy adult persons in twenty-four hours, only 0.66 grammes, which is scarcely one tenth of the average of chlorine actually removed by the urine. From this it is evident that the mode of determining the fixed salts by incineration of the residue of the urine after evaporation is quite useless for analytical purposes, as are also the whole of the analyses made by that method. But even were the analyses by incineration approximatively correct, yet evaporation and incineration take so much trouble and time, that the process is entirely unavailable for practical purposes. These reasons are